System and method for embedding a sub-channel in a block coded data stream

ABSTRACT

The present invention relates in general to a method, apparatus, and article of manufacture for providing high-speed digital communications through a communications channel. In one aspect, the present invention employs a variable rate back channel, incorporated within an existing communication that does not increase or adversely impact the transmission rate of data on the communication channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional PatentApplication Serial No. 60/313,456, entitled “Variable Rate Sub-ChannelUsing Block Code RDS”, filed Aug. 20, 2001, and U.S. ProvisionalApplication Serial No. 60/313,214, entitled “Transceiver Apparatus andMethod”, filed Aug. 17, 2001. The contents of these provisionalapplications are incorporated, in their entirety, by reference herein.

[0002] This application is related to U.S. Provisional PatentApplication Serial No. 60/313,454, entitled “Transceiver System for HighSpeed Digital Signaling”, filed Aug. 20, 2001 (Docket No.13764.2-US-P1); U.S. Provisional Patent Application Serial No.60/313,455, entitled “Automatic Slicer Level Adaption”, filed Aug. 20,2001 (Docket No. 13764.3-US-P2); U.S. Provisional Patent ApplicationSerial No. 60/313,478, entitled “Variable Delay FIR Equalizer for SerialBaseband Communications”, filed Aug. 20, 2001 (Docket No.13764.5-US-P1); U.S. Provisional Patent Application Serial No.60/313,477, entitled “Crosstalk Management for High-Speed SignalingLinks”, filed Aug. 20, 2001 (Docket No. 13764.6-US-P1); and U.S.Provisional Patent Application Serial No. 60/313,476, entitled “Methodand Apparatus for Encoding and Decoding Digital Communications Data”,filed Aug. 20, 2001 (Docket No. 13764.7-US-P1). All of these provisionalapplications are hereby incorporated herein by reference.

[0003] This application is also related to non-provisional patentapplications that claim priority to one or more of the above-referencedprovisional patent applications. These non-provisional patentapplications are entitled “System and Method for High Speed DigitalSignaling”, filed Aug. 16, 2002 (Docket No. 209.001-US); entitled“System and Method for Slicer Level Adaption”, filed Aug. 16, 2002(Docket No. 209.002-US); “System and Method for Providing Variable DelayFIR Equalizer for Serial Baseband Communications”, filed Aug. 16, 2002(Docket No. 209.004-US); “System and Method for Providing CrosstalkManagement for High-Speed Signaling Links”, filed Aug. 16, 2002 (DocketNo. 209.005-US); and “Method and Apparatus for Encoding and DecodingDigital Communications Data”, filed Aug. 16, 2002 (Docket No. 209.006).The aforementioned non-provisional patent applications are herebyincorporated by reference, in their entirety, herein.

BACKGROUND OF THE INVENTION

[0004] This application relates in general to a method, apparatus, andarticle of manufacture for providing high-speed digital communicationsthrough a communications channel, and more particularly to a method,apparatus, and article of manufacture for providing a system and methodfor embedding a sub-channel in a block coded data stream.

[0005] Digital communications systems are continuously increasing thetransfer rate at which data is transmitted between devices through acommunications channel, for example, a backplane. One technique forincreasing the data transfer rate is to encode the data prior totransmission. In this regard, there are a number of techniques forencoding data. Many of these techniques utilize different numbers ofsignals and modulation of symbols in order to increase the data transferrate. One such method of modulating symbols is to use a multi-levelpulse amplitude modulation (PAM-n) scheme that encodes a plurality ofbits of data into or onto a single signal in which the symbols arerepresented as a set of signal levels between minimum and maximum signallevels. An n-level pulse amplitude modulation technique may result in atransmitted symbol rate that is (log (2)/log (n)) of the actual datatransmission rate.

[0006] In certain data communications systems, adaptive controls areemployed to facilitate proper decoding of the received signal to therebyrecover the digital representation of the data bits being transmitted.These adaptive controls adjust or modify various operating parameters oftransmitters and receivers of the data communications system. Theseparameters may be best determined using the specific topography andoperating characters of the communications channel. In addition, theseparameters tend to change over time and, as such, adaptively controllingthe transmitters and receivers may enhance the operating performance ofthe communications system as that system changes over time.

[0007] When adaption is performed at the transmitter, there exists aninherent problem of communication. Any measure of performance can onlybe determined at the receiver, which is at the far end of the link.Therefore, information collected at the receiver must be returned backto the transmitter to adapt the output signal characteristics of thetransmitter. The information sent from the receiver back to thetransmitter to modify, change, optimize and/or enhance the output signalcharacteristics of the transmitter in accordance with the signalreceived by the receiver is termed a back channel.

SUMMARY OF THE INVENTION

[0008] The present invention relates in general to a method, apparatus,and article of manufacture for providing high speed digitalcommunications through a communications channel, and more specificallyto a system and method for providing a variable rate back channel(incorporated within an existing communication) without increasing oradversely impacting the transmission rate of data on the channel and/orwithout utilizing any or a significant portion of the bandwidthoriginally associated with that channel.

[0009] It should be noted that although the detailed description tofollow describes the invention in the context of four-level pulseamplitude modulation (PAM-4), unless otherwise noted, the systems andtechniques described are applicable to any and all modulation schemesincluding but not limited to PAM-4 encoding. Indeed, all forms ofmodulation, whether now known or later developed, are intended to bewithin the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the course of the detailed description to follow, referencewill be made to the attached drawings. These drawings show differentaspects of the present invention and, where appropriate, referencenumerals illustrating like structures, components and/or elements indifferent figures are labeled similarly. It is understood that variouscombinations of the structures, components and/or elements other thanthose specifically shown are contemplated and within the scope of thepresent invention.

[0011]FIG. 1 illustrates an exemplary communications channel between twodigital processing devices according to one possible embodiment in whichthe invention operates;

[0012]FIG. 2 illustrates an exemplary communications channel accordingto an embodiment of the present invention;

[0013]FIG. 3 illustrates a block diagram of a channel/subchannelsubsystem according to an example embodiment of the present invention;and

[0014]FIG. 4 illustrates an example arrangement for RDS block codesaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

[0015] In the following detailed description of exemplary embodiments ofthe invention, reference is made to the accompanied drawings, which forma part hereof, and which is shown by way of illustration, specificexemplary embodiments of which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the invention is defined only by theappended claims.

[0016] Throughout the specification and claims, the following terms takethe meanings explicitly associated herein, unless the context clearlydictates otherwise. The term “connected” means a direct connectionbetween the items connected, without any intermediate devices. The term“coupled” means either a direct connection between the items connected,or an indirect connection through one or more passive or activeintermediary devices. The term “circuit” means either a single componentor a multiplicity of components, either active and/or passive, that arecoupled together to provide a desired function. The term “signai” meansat least one current, voltage, or data signal. The term “module” means acircuit (whether integrated or otherwise), a group of such circuits, aprocessor(s), a processor(s) implementing software, or a combination ofa circuit (whether integrated or otherwise), a group of such circuits, aprocessor(s) and/or a processor(s) implementing software.

[0017]FIG. 1 illustrates an exemplary communications channel between twodigital processing devices according to one embodiment of the presentinvention. Digital processing devices 101 and 102, such as personalcomputers, communicate with each other by transmitting digital signalsthrough communications channel 100. In one embodiment, a digitalrepresentation of the data to be transmitted is encoded and transformedinto an electronic signal capable of passing through communicationschannel 100. The electronic signal is transmitted by transmitter 110 toreceiver 111. The received electronic signal, which may be distortedwith respect to the electronic signal transmitted into or onto thechannel by transmitter 110, is processed and decoded by receiver 111 toreconstruct a digital representation of the transmitted information.

[0018] The communications channel 100 may be, for example, constructedusing one or more cables, wires, traces or the like, or may be part of abackplane, or may be a wireless communications medium through which thesignal passes from transmitter 110 to receiver 111. One skilled in theart will recognize that any such communications media, when used inconjunction with a corresponding transmitter/receiver pair appropriatefor a particular medium, may be used to construct a communicationschannel in accordance with the present invention. For example, otherchannels that may be implemented in the present invention includeelectronic, optical or wireless. Indeed, all types of channels ofcommunication (i.e., communication channels), whether now known or laterdeveloped, are intended to be within the scope of the present invention.

[0019]FIG. 2 illustrates an exemplary communications channel accordingto one embodiment of the present invention. The communications channel100 enables or facilitates transmission of information betweenassociated pairs of transmitters and receivers, for example, transmitter110 and receiver 111. In one embodiment, transmitter 110 and receiver111 employ a four level pulse amplitude modulated (PAM-4) communicationstechnique to send two bits of data through channel 100. That is, thetransmitter/receiver pair is used to send two bits of data for eachsymbol transmitted through the channel 100. A ten bit word is loadedinto parallel-to-serial register 211 with the output of the registerbeing a two bit pair that is transmitted through channel 100. Oncereceived, the sequence of two bit codes are loaded intoserial-to-parallel register 212 to reconstruct or decode the ten bitword.

[0020] The system employs a plurality of transmitter and receiver pairs,each transmitter and receiver pair using a PAM-4 communication scheme tosend the two bits of data through channel 100. Moreover, eachtransmitter and receiver pair operates in the same manner to send datathrough channel 100 in a serial fashion that “packages” two bits intoone single symbol. Five successive symbols are used to send the ten bitcoded representation of the underlying, sparsely populated, nine bituser data byte. The overhead associated with mapping the sparselypopulated nine bit user data to ten bits is typically utilized to ensureadequate timing information within the transmitted data and to controlthe Running Digital Sum (RDS) of the transmitted data stream.

[0021] Briefly, the RDS may be characterized as the digital integrationof the transmitted symbols. A purpose of RDS control is to reduce thelow frequency content of the transmitted signal, thereby widening thespectral null at DC. A common example is 8B10B encoding.

[0022] Although the present invention is described in the context ofPAM-4 communications technique, the present invention may utilize othermodulation formats that encode fewer or more bits per symbol codes basedon other than byte wide user may be readily adapted or employed.Moreover, as mentioned above, other communication mechanisms that usedifferent encoding tables, other than four levels, or use othermodulation mechanisms may also be used. For example, 8B10B, PAM-5,PAM-8, PAM-16, CAP, and wavelet modulation may be utilized in thepresent invention. The techniques described herein are applicable to anyand all modulation schemes, including but not limited to PAM-4 encodingdescribed herein. Indeed, all types of modulation formats and modulationor encoding schemes, whether now known or later developed, are intendedto be within the scope of the present invention.

[0023]FIG. 3 illustrates one possible point-to-point network topologyaccording to one embodiment of the present invention. In thisembodiment, the communications system comprises a pair of transceivers(i.e., XCVR ‘A’ and XCVR ‘B’) connected in a point-to-point fashion,transmitting and receiving coded data, with each transmitter (i.e., TX‘A’ and TX ‘B’) including an adaptive transmit equalizer. Here, thesystem employs two modes of operation including (1) Normal Operation and(2) Initialization Phase. In the Normal Operation, the system uses thecommunication channel to transmit and receive user data.

[0024] In the Initialization Phase, no user data is being transmitted;rather, the system uses the communication channel to set-up, initialize,or re-initialize various aspects, components or modules of the system,for example, the adaptive equalizer in the transmitter. TheInitialization Phase may occur, for example, during power-up or during aREACQ (re-acquire) command. In response, a transceiver system acquiresand retains control of the channel thereby prohibiting user data frombeing sent. During this time the transceivers may use anAuto-Negotiation (AN) protocol to transfer, for example, coefficientinformation for use by the transmit equalizer. This information isdetermined or calculated by a receiver module (for example, RX ‘B’) andsent to its associated transmitter module (TX ‘A’) that contains theadaptive transmitter equalizer. At the conclusion of the InitializationPhase, Normal Operation commences and control of the channel is released(user data transmission may commence).

[0025] It should be noted that the Auto-Negotiation protocol isdescribed in detail in U.S. Provisional Patent Application Serial No.60/313,454, entitled “Transceiver System for High Speed DigitalSignaling”, filed Aug. 20, 2001 (Docket No. 13764.2-US-P1) andnon-provisional patent application entitled “System and Method for HighSpeed Digital Signaling”, filed Aug. 16, 2002 (Docket No. 209.001-US).As mentioned above, these applications are incorporated herein byreference in their entirety.

[0026] It should be further noted that, during Normal Operation, changesin the channel characteristics or transmission characteristics of thedata, caused, for example, by temperature changes, may affect theoptimum value of the coefficients in the adaptive transmit equalizersunder these circumstances, new coefficient data is determined by andsent from the receiver module to the adaptive equalizer module in theassociated transmitter module during normal operation to permit “slow”adaption of coefficients without interrupting the transmission of userdata. The “overlaid” control channel is also referred to as a backchannel.

[0027] The revised or new coefficient data (including data pertaining tothe roving tap(s), if any) may be continuously, periodically orintermittently determined or calculated by the receiver module.Similarly, the revised or new coefficient data (including datapertaining to the roving tap(s), if any) may be continuously,periodically or intermittently transmitted to the associated transmittermodule. For example, with reference to FIG. 3, receiver module RX ‘B’may continuously determine or calculate new coefficient data for theadaptive transmit equalizer in transceiver ‘A’ (i.e., XCVR ‘A’) due tochanges in the transmission environment of, for example, thecommunications channel. In response, the transmitter TX ‘B’ oftransceiver ‘B’ (i.e., XCVR ‘B’) may continuously, periodically orintermittently transmit that information via the back channel to thereceiver RX ‘A’ of transceiver ‘B’. The new coefficient data is thenimplemented in the adaptive equalizer to enhance the overall operationof the communications system.

[0028] In particular, with reference to FIG. 3, RX ‘B’ may determinethat TX ‘A’ is no longer operating optimally, efficiently or adequately.In response, RX ‘B’ instructs TX ‘A’ on how to transmit informationacross the link to RX ‘B’, under the current operating conditions orenvironment, such that some cost function of error is minimized. In oneembodiment, the information from RX ‘B’ is carried back to TX ‘A’ byfirst transferring the information to TX ‘B’ via an internal connectionwithin the die (of the integrated circuit device) that constitutes XCVR‘B’. In response, XCVR ‘B’ encodes the message and places it into theback channel. The back channel is sent with the user data in the up-linkfrom TX ‘B’ to RX ‘A’. Finally, the message contained within the backchannel of the up-link is decoded by digital hardware in RX ‘A’ andprovided to digital hardware that controls the adaptive equalizer in TX‘A’. The digital hardware in TX ‘A’ adopts the corrections or implementsthe new operating parameters (for example, adaptive equalizer tapadjustments) that were contained in the back channel message by changingthe settings of the adaptive equalizer in TX ‘A’. This completes thefeedback path from RX ‘B’ to TX ‘A’.

[0029] Similarly, a connection from RX ‘A’ to TX ‘B’ is formed via theback channel in the other link. That is, XCVR ‘A’ encodes the messageand places it into the back channel. That message is received anddecoded by RX ‘B’ and provided to digital hardware that controls theadaptive equalizer in TX ‘B’. TX ‘B’ incorporates the corrections orimplements the new operating parameters by changing the settings of itsadaptive equalizer.

[0030] It should be noted that other physical connections for the backchannel may also be used—such as a shelf software loop which caninterrogate both XCVR ‘B’ and XCVR ‘A’. The back channel may also beimplemented using a physically separate route from receiver totransmitter (either within the same media carrying the information fromthe transmitter to receiver, or through any other pathway including asoftware link that can be running above the current protocol), or as isthe case in this invention, be placed within the bi-directionaldata-path that already exists. The present embodiment utilizes theexisting bi-directional user paths to form the back channel and does sowithout impact to, or serious degradation of the user data bandwidth. Inthis regard, in one aspect, the present invention details how the backchannel information is encoded and decoded without interrupting, orseriously degrading the user data flow.

[0031] In another aspect, the present invention describes a system andmethod of using block codes, with RDS control, to transmit additionaldata from the receiver module to the far-end transmitter module. In RDScontrol systems, there exist user data word for which there are multiplecoded representations with differing weights (sum of the codedrepresentations), the choice of which coded representation to transmitis based upon driving the RDS to zero. For example, if a user data wordthat is to be transmitted has two coded representations, one with apositive weight and one with a negative weight and the present value ofthe RDS is positive, then the encoder selects the negative weight codedrepresentation to be transmitted. If the present value of the RDS isnegative, then the encoder selects the positive weight codedrepresentation to be transmitted. The receiver, upon receiving either ofthese coded representations, maps the received information back into theuser data word.

[0032] In one embodiment of this aspect of the present invention, one ormore user blocks are designated as special user blocks; all special userblocks having multiple coded representations. When a special user blockis the input to the encoder, the state of the RDS is not used to selectwhich code word to transmit. Instead, selection is based upon the stateof the back channel information to be transmitted. For example, if aspecial user block has two coded representations, then it can be used totransmit one bit of back channel information.

[0033] It may be advantageous to choose a special user code so that theback channel data frame transmission occurs on average with somefrequency of R codes per second. In this way, the resulting back channelbit rate (in the case of a one user code to two back channel codes) onaverage will be R bits per second (bps). In a more general case of oneuser code to n back channel codes, the resultant back channel rate willbe R times log(n)/log(2) bps. It should be noted that if there is no wayto guarantee (with a high degree of certainty) that a special user blockword will occur at some rate R, then it may be possible to statisticallyconstruct such a case by employing a scrambler. In this regard, thescrambler is used to scramble the user data words. Thus, even if asingle user data word is repeatedly input to the system, the output ofthe scrambler will “utilize” or “walk through” the entire code space.

[0034] One embodiment of the present invention is to encode a subset ofthe user data words into two coded representations and the complement ofthe user data words into single coded representations. A subset of theuser data words with two coded representations are designated as specialuser data words. In the simplest form, only one special user data wordis designated.

[0035] A ROM, EPROM, EEPROM (or the like) may be used to hold ormaintain the encoding table. In one embodiment, the ROM has two columnsand as many rows as there are unique user data words (for eight bit userdata words there would be two hundred fifty-six rows). Each row of theROM contains the coded representations for a particular user data wordand the weights of the coded representations. The weights stored astwo's complement numbers. The user data word is first input to ascrambler, and the output of the scrambler forms the input to theencoding table. If the scrambled user data word has only a single codedrepresentation, then that coded representation is stored in bothcolumns. The selection of which column of the ROM to use is controlledby a multiplexer (“MUX”) that has two inputs: the sign of the RDS andthe next back channel bit to be sent.

[0036] Preceding the ROM, the user data word is delayed through a singlestage, which may be realized by a bank of flip-flops, and is checked todetermine if it is a special user data word. If it is a special userdata word, the MUX is configured to select the back channel bit as itsoutput, and the register holding the back channel bit is loaded with thenext bit to be sent. If the scrambled user data word is not a specialuser data word, then the MUX is configured to select the sign of the RDSas its output. The weight of the transmitted coded representation, as atwo's complement number, is added to the RDS accumulator.

[0037] In the preferred embodiment, the RDS accumulator is a saturatingup/down counter, for example, an eight bit saturating up/down counter.In the receiver, when one of the coded representations of a special userblock is received, it is mapped to the scrambled user data word and theback channel bit is extracted. The output of the decoding table ispassed through a complementary descrambler to recover the unscrambleduser data word.

[0038] In a preferred embodiment, the left hand column of the ROMcorresponds to a “0” for the back channel bit and the right hand columnof the ROM corresponds to a “1” for the back channel bit. In oneembodiment, the back channel bits are part of a back channel frame andthe receiver loads the received bit into the next position in the frame.The frame contains pieces that indicate the tap adjustment commands foreach tap of the equalizer. When an entire frame is constructed it ischecked for validity. If valid, the tap adjustments embedded in theframe are passed across a digital bus to the digital hardware thatcontrols the adaptive transmit equalizer. The digital hardware receivesthe commands and makes the adjustments to the taps of the adaptivetransmit equalizer.

[0039]FIG. 4 illustrates a preferred embodiment of the proposed encodingin which the special back channel code is the one dual code with RDS=1.As can be seen from FIG. 4, there are a total of 256+6=262 user codewords. A purpose of the scrambler is to arrange for a pseudo randomselection of the 262 valid user codes based upon the incoming user code.By doing this, if the user code rate is U codes per second, and thepseudo random scrambler is evenly weighted, then each code word,including the special back channel code, will occur with a statisticalregularity of U/262 codes per second. With the special back channel codenow occurring with a rate of U/262 codes per second on average, the backchannel will have a bit rate of U*log(n)/262/log(2) bits per second.Finally, for the embodiment depicted in FIG. 4, n=2 and the back channelbit rate will be U/262 bps.

[0040] Thus, in this embodiment, the resultant data rate for the backchannel is variable and may be suitable for slow adaption control of thedata communications channel. In addition, the use of embedding the backchannel within the coding table does not interrupt, limit or impair thetransmission of user data. In fact, the use of this sub-channel forcontrol data may be completely transparent to the user.

[0041] It should be noted that other methods to include a back channelwithin the code space are possible, and include but are not limited to:Zero RDS Selection and Running RDS Selection. For example, Zero RDSSelection is applicable in code spaces in which it is possible to havezero weight coded representations, for example, 8B10B. The special userdata words are assigned two zero weight coded representations. One codedrepresentation is assigned to a back channel bit of ‘0’ while the otheris assigned to a back channel bit of “1”. Whenever a special user datawords, mapped in this way, is encountered during transmission, a backchannel bit can be sent The receiver decodes both coded representationsas the same user data word and also decodes the corresponding backchannel bit. Note that in general, not all codes have a zero RDS, so thereceiver may only perform this back channel decode when a zero weightcoded representation is received.

[0042] In a Running RDS selection, not all block code combinations havezero RDS block words. Typically, for an m-to-k block code, if k is odd,the resulting blocks can only have non-zero RDS values, i.e., 8B5Q codewhich maps eight binary bits into five quaternary symbols. Here theweights of the coded representations is:

[0043] 15, 13, 11, 9, 7, 5, 3, 1, −1, −3, −5, −7, −9, −11, −15.

[0044] In this case, user data words may be paired in balanced codedrepresentations (i.e., one coded representation with RDS=+1 and onecoded representation with RDS=−1). Once coded representations have beenassigned, the transmitter controls the DC content of the line by keepinga running sum of the transmitted block RDS values and selecting fromeither the positive or negative columns in order to drive thetransmitted RDS towards zero. Thus, whenever the transmitted RDS hitszero, the user is free to select the next block code's RDS. The backchannel bit is encoded into this selection (i.e., if the RDS=+1 then theback channel bit=1, and if the RDS=−1 then the back channel=0).

[0045] This method requires that the running digital sum at both thetransmitter and receiver be synchronized and remain synchronized (or bere-synchronized, for example, periodically or intermittently). At thereceiver module, a running digital sum is computed. Whenever the sumhits “0”, the RDS of the next received code word contains the encodedback channel bit. Here the probability may be more complicated anddependent upon the code space and the maximum values of the block RDSvalues.

[0046] Finally, TABLE 1 is a code table that may be employed in thepresent invention. The weights of the coded representations are notindicated below; rather the weights are the sum of the symbols of thecoded representations. TABLE 1 is simply one possible implementation ofa plethora of possible implementations. TABLE 1 8B5QSMB Code AssignmentDecimal Q Code Q Code Decimal Q Code Q Code Decimal Q Code Q Code CodeRDS >0 RDS <0 Code RDS >0 RDS <0 Code RDS >0 RDS <0 Back Channel Code 85 −3-1311 171 −1-1131  1 −3-1131 31-1-3-1  86 −31111 172 1-3131 RDSBalancing Codes  87 111-3-1 173 −11-131  2 −11331 1-1-3-3-1  88 −131-3-1174 1-1-131  3 1-1331 −11-3-3-1  89 31-3-1-1 175 −31311  4 −131311-3-1-3-1  90 3-1-1-1-1 176 −1-1311  5 11131 −1-1-1-3-1  91 1-3111 177−11111  6 3-1131 −31-1-3-1  92 −11-111 178 1-1111  7 13-131 −1-31-3-1 93 1-1-111 179 −13-111  8 31-131 −3-11-3-1  94 11-311 180 11-111  9−13311 1-3-3-1-1  95 3-1-311 181 3-1-111 10 11311 −1-1-3-1-1  96 −313-11182 31-311 11 3-1311 −31-3-1-1  97 −1-13-11 183 −113-11 12 13111−1-3-1-1-1  98 −13-1-1-1 184 1-13-11 13 31111 −3-1-1-1-1  99 1-11-1-1185 −131-11 14 33-111 −3-31-1-1 100 −111-1-1 186 111-11 15 133-11−1-3-31-1 101 −1-13-1-1 187 3-11-11 16 313-11 −3-1-31-1 102 −313-1-1 18813-1-11 17 331-11 −3-3-11-1 103 3-1-31-1 189 31-1-11 18 −1333-1 1-3-3-31104 11-31-1 190 131-31 19 1133-1 −1-1-3-31 105 −13-1-11 191 311-31 203-133-1 −31-3-31 106 1-311-1 192 33-1-31 21 1313-1 −1-3-1-31 1073-1-1-11 193 −3133-1 22 3113-1 −3-1-1-31 108 31-3-11 194 −1-133-1 2333-13-1 −3-31-31 109 −131-31 195 −1113-1 24 1331-1 −1-3-3-11 110 111-31196 1-113-1 25 3131-1 −3-1-3-11 111 3-11-31 197 −13-13-1 26 3311-1−3-3-1-11 112 13-1-31 198 11-13-1 27 333-1-1 −3-3-311 113 31-1-31 1993-1-13-1 28 −13331 1-3-3-3-1 114 −3-133-1 200 −1131-1 29 11331−1-1-3-3-1 115 −3113-1 201 1-131-1 30 3-1331 −31-3-3-1 116 −1-113-1 202−1311-1 31 13131 −1-3-1-3-1 117 1-313-1 203 1111-1 32 31131 −3-1-1-3-1118 −11-13-1 204 3-111-1 33 33-131 −3-31-3-1 119 1-1-13-1 205 13-11-1 3413311 −1-3-3-1-1 120 −3131-1 206 31-3-3-1 35 31311 −3-1-3-1-1 121−1-131-1 207 3-1-1-3-1 36 33111 −3-3-1-1-1 122 −1111-1 208 11-1-3-1 37333-11 −3-3-31-1 123 1-111-1 209 −13-1-3-1 38 1333-1 −1-3-3-31 124−13-11-1 210 1-11-3-1 39 3133-1 −3-1-3-31 125 11-11-1 211 −111-3-1 403313-1 −3-3-1-31 126 3-1-11-1 212 3-1-3-1-1 41 3331-1 −3-3-3-11 12731-31-1 213 11-3-1-1 42 13331 −1-3-3-3-1 128 −113-1-1 214 1-1-1-1-1 4331331 −3-1-3-3-1 129 1-13-1-1 215 −11-1-1-1 44 33131 −3-3-1-3-1 130−131-1-1 216 1-31-1-1 45 33311 −3-3-3-1-1 131 111-1-1 217 −1-11-1-1 46−31331 3-1-3-3-1 132 3-11-1-1 218 −311-1-1 47 −1-1331 11-3-3-1 13313-1-1-1 219 −3-13-1-1 48 −11131 1-1-1-3-1 134 31-1-1-1 220 1-1-31-1 491-1131 −11-1-3-1 135 131-3-1 221 −11-31-1 50 −13-131 1-31-3-1 136311-3-1 222 1-3-11-1 51 11-131 −1-11-3-1 137 33-1-3-1 223 −1-1-11-1 523-1-131 −311-3-1 138 −3111-1 224 −31-11-1 53 −11311 1-1-3-1-1 139−3-131-1 225 −1-311-1 54 1-1311 −11-3-1-1 140 1-3-13-1 226 −3-111-1 55−13111 1-3-1-1-1 141 −1-1-13-1 227 −1-3-13-1 56 3-1111 −31-1-1-1 142−31-13-1 228 −3-1-13-1 57 13-111 −1-31-1-1 143 −1-313-1 229 −3-313-1 5831-111 −3-11-1-1 144 −3-113-1 230 3-1-3-31 59 −133-11 1-3-31-1 14531-3-31 231 11-3-31 60 113-11 −1-1-31-1 146 3-1-1-31 232 1-1-1-31 613-13-11 −31-31-1 147 11-1-31 233 −11-1-31 62 131-11 −1-3-11-1 148−13-1-31 234 1-31-31 63 311-11 −3-1-11-1 149 1-11-31 235 −1-11-31 6433-1-11 −3-311-1 150 −111-31 236 −311-31 65 331-31 −3-3-13-1 1513-1-3-11 237 1-1-3-11 66 −1133-1 1-1-3-31 152 11-3-11 238 −11-3-11 671-133-1 −11-3-31 153 1-1-1-11 239 1-3-1-11 68 −1313-1 1-3-1-31 154−11-1-11 240 −1-1-1-11 69 1113-1 −1-1-1-31 155 1-31-11 241 −31-1-11 703-113-1 −31-1-31 156 −1-11-11 242 −1-31-11 71 13-13-1 −1-31-31 157−311-11 243 −133-1-1 72 31-13-1 −3-11-31 158 −3-13-11 244 113-1-1 73−1331-1 1-3-3-11 159 1-1-311 245 3-13-1-1 74 1131-1 −1-1-3-11 160−11-311 246 131-1-1 75 3-131-1 −31-3-11 161 1-3-111 247 311-1-1 761311-1 −1-3-1-11 162 −1-1-111 248 33-1-1-1 77 3111-1 −3-1-1-11 163−31-111 249 331-3-1 78 3-3-11-1 −3-31-11 164 −1-3111 250 1-3-311 79133-1-1 −1-3-311 165 −3-1111 251 −1-1-311 80 313-1-1 −3-1-311 166−1-3-131 252 −31-311 81 −1-3131 167 −3-1-131 253 −1-3-111 82 13-1-3-1168 −3-3131 254 −3-1-111 83 −1-1-131 169 −3-1331 255 −3-3111 84 1-3-131170 −31131 256 −3-3-131

[0047] TABLE 2 Special Characters (“K” Codes) and Supported “K” CodesQ4<1:0>-Q0<1:0> Binary Value Q Code Q Code Code Description <7:0> RDS >0 RDS < 0 Special Characters K 28.0 Skip (aka Idle, aka ∥R∥) 0 0 0 1 1 10 0 −3 1−1 3 1  3−1 1−3−1 K 28.5 Sync (aka Idle, aka ∥K∥) 1 0 1 1 1 1 00 −1−1 1 1 1  1 1−1−1−1 K 27.7 Start 1 1 1 1 1 0 1 1 −1 1 1−1 1 1−1−1 1−1 K 29.7 Terminate 1 1 1 1 1 1 0 1  1−1 1−1 1 −1 1−1 1−1 K 30.7Error 1 1 1 1 1 1 1 0  1 1−1−1 1 −1−1 1 1−1 Accelerant Control CodesSI−K 23.7 1 1 1 1 0 1 1 1  3 3 3 3−1 −3−3−3−3 1 Error 1 1 1 1 1 1 1 1−1−1−1−1−1  1 1 1 1 1

[0048] In one embodiment, the case of RDS balancing codes with a decimalcode between two and eighty inclusive, the selection of which codedrepresentation to send is based upon driving the RDS to zero, as isdescribed in U.S. Provisional Patent Application Serial No. 60/313,476,entitled “Method and Apparatus for Encoding and Decoding DigitalCommunications Data”, filed Aug. 20, 2001 (Docket Number 13764.7-US-P1)and U.S. Patent Application entitled “Method and Apparatus for Encodingand Decoding Digital Communications Data”, filed Aug. 16, 2002 (DocketNo. 209.006-US).

[0049] In the case of unbalanced RDS codes with a decimal value betweeneighty-one and two hundred fifty-six, the single coded representation issent regardless of RDS state. For the case of special decimal code “1”,RDS state is not used for selecting which coded representation totransmit. Instead, if the current back channel state to be transmittedhas a binary value of “1”, then the “−3 −1 1 3 1” coded representationis transmitted. If the current back channel state to be transmitted hasa binary value of “0”, then the “3 1 −1 −3 1” coded representation istransmitted.

[0050] At the receiver, upon reception of either “−3 −1 1 3 1” or “3 1−1 −3 −1” the decimal code “1” is output to the user data stream.However, in the case of reception of coded block “−3 −1 1 3 1” a “1” isoutput to the back channel data stream. Finally, in the case ofreception of coded block “3 1 −1 −3 −1” a “0” is output to the backchannel data stream.

[0051] In one embodiment, special codes (K codes) are all mapped tobalanced coded representations. Both coded representations have the samesymbol magnitudes but the symbols in one representation are of oppositesign of those in the other representation. Thus, for each K code theweight of each coded representation is equal in magnitude but oppositein sign to the other. Each time a K code is to be transmitted, a singlebit of the scrambler is used to select the RDS value. When the scramblerbit is “1” the positive weight coded representation is transmitted. Whenthe scrambler bit is “0” the negative weight coded representation istransmitted. The weight of the special code is added to RDS accumulator.The K23.7 is the 8B10B Carrier Extend K code. Whenever there is a lackof data to send the channel may be idled by sending random data. Thismay be accomplished by simply providing any fixed pattern to thetransmit user interface. This data will be scrambled and transmittedduring the idle time. The back channel will be preserved since the backchannel code is among the codes that will result from scrambling. Thus,optimal equalization may be maintained even if there is no input data.

[0052]FIG. 1 illustrates an example of a suitable operating environmentin which the invention may be implemented. The operating environment isonly one example of a suitable operating environment and is not intendedto suggest any limitation as to the scope of use or functionality of theinvention. Other well known computing systems, environments, and/orconfigurations that may be suitable for use with the invention include,but are not limited to, network equipment, backplanes, communicationsequipment, personal computers, server computers, hand-held or laptopdevices, multiprocessor systems, microprocessor-based systems,programmable consumer electronics, network PCs, minicomputers, mainframecomputers, distributed computing environments and data communicationequipment that include any of the above systems or devices, and thelike.

[0053] The invention may also be described in the general context ofcomputer-executable instructions, such as program modules, executed byone or more computers or other devices. Generally, program modulesinclude routines, programs, objects, components, and data structuresthat perform particular tasks or implement particular abstract datatypes. Typically, the functionality of the program modules may becombined or distributed. All such combinations or distributions, nowknown or later developed, are within the scope of the present invention.

[0054] A processing device coupled to a communications channel 100 (viatransceivers) typically includes at least some form of computer readablemedia. Computer readable media can be any available media that can beaccessed by these devices. By way of example, and not limitation,computer readable media may comprise computer storage media andcommunication media. Computer storage media includes volatile andnonvolatile, removable and non-removable media implemented in any methodor technology for storage of information such as computer readableinstructions, data structures, program modules or other data. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, BC-ROM, digital versatile disks (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices, or any other mediumwhich can be used to store the desired information and which can beaccessed by processing devices.

[0055] Communication media typically embodies computer readableinstructions, data structures, program modules or other data in amodulated data signal such as a carrier wave or other transportmechanism and includes any information delivery media. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, RF, infrared and otherwireless media.

[0056] Additionally, the embodiments described herein may be implemented(in part) as logical operations performed by programmable processingdevices. The logical operations of these various embodiments of thepresent invention are implemented (1) as a sequence of computerimplemented steps or program modules running on a computing systemand/or (2) as interconnected machine modules or hardware logic withinthe computing system. Accordingly, the logical operations making up theembodiments of the invention described herein can be variously referredto as operations, steps, or modules.

[0057] While the above embodiments of the present invention describe asystem and method for embedding a sub-channel in a block coded datastream, one skilled in the art will recognize that the use of aparticular coding arrangement is merely an example embodiment of thepresent invention. It is to be understood that other embodiments may beutilized and operational changes may be made without departing from thescope of the present invention as recited in the attached claims.

[0058] As such, the foregoing description of the exemplary embodimentsof the invention has been presented for the purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not with this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A system for providing a bi-directional datacommunications channel having a user data channel and a back channelwithin each direction of the bi-directional data communications channel,the system comprising: at least two transmitter modules, one transmittermodule for each direction of the bi-directional data communicationschannel, each of the transmitter modules encode a user data stream andback channel data stream into a coded data stream and transmit the codeddata stream through the communications channel; and at least tworeceiver modules, one receiver module for each direction of thebi-directional data communications channel, each of the receiver modulesreceive the coded data stream transmitted through the data channel anddecodes the coded data stream into the user data stream and the backchannel data stream.
 2. The system according to claim 1 wherein the userdata stream includes at least one user data word that corresponds to aplurality of coded representations wherein each of the codedrepresentations represents a symbol of the back channel data stream, andwherein each receiver module, upon receiving at least one of theplurality of coded representations that represents back channelinformation, decodes the coded representation into the user data wordfor the user data channel and into the symbol for the back channel datastream.
 3. The system according to claim 2, wherein the back channeldata is transmitted as a serial stream of symbols within a data frame.4. The system according to claim 3, wherein the back channel datacomprises channel performance information to allow continuous orperiodic adaption of operation of the communications channel.
 5. Thesystem according to claim 3 where the communications channel includes abackplane.
 6. The system according to claim 3 where the communicationschannel includes a cable.
 7. The system according to claim 2, wherein asecond plurality of code words that correspond to back channelinformation is incorporated into the coded, transmitted data stream whenback channel data symbols have not been transmitted within a predefinedamount of time to ensure a minimum back channel data rate
 8. The systemaccording to claim 7, wherein each receiver module, upon receiving oneof the plurality of code words that represents back channel information,decodes for the back channel data stream.
 9. The system according toclaim 2, wherein the back channel is used to establish a control channelto a far-end module of a link and wherein the back channel is controlledby a near-end module.
 10. The system according to claim 2, wherein theback channel is used to provide additional channel bandwidth that may bemapped to another communications channel.